A concise review of vaccines against Mycoplasma hyopneumoniae

Effect of vaccination against Mycoplasma hyopneumoniae on divergent pig genetic groups

The bacterium Mycoplasma hyopneumoniae (Mhp) causes a chronic infectious respiratory disease in pigs, leading to important economic losses. This study aimed to compare the immune response of the local Piau breed and a commercial line to Mhp vaccination. For this, two phases were carried out. In the first, gene expression of toll-like receptors (TLR2, TLR4, TLR6, and TLR10) and cytokines (IL2, IL6, IL8, IL10, IL12, IL13, TNFα, and TGFβ) was assessed in porcine blood mononuclear cells (PBMC) from the two genetic groups before and after vaccination. In the second experiment, nitric oxide production, specific antibodies, and gene expression of toll-like receptors and cytokines were evaluated in bronchoalveolar lavage fluid (BALF) cells of vaccinated and unvaccinated pigs. After vaccination against Mhp, TLR2, TLR4, TLR6, TLR10, IL6, TNFα, and TGFβ expression levels were elevated in PBMC from commercial animals, and TLR6, TLR10, and TGFβ expression levels were elevated in PBMC from the Piau group. Vaccination also increased the production of Mhp-specific IgG antibodies in BALF cells in the Piau breed. Comparison of the two genetic groups revealed differences in TNFα and IL10 expression in BALF cells. These results show that Piau pigs have different immune responses to vaccination compared with commercial animals. It is worth noting that these genetic differences between both genetic groups may be related to phenotypic differences in Mhp resistance or susceptibility.

Research Progress on Immune Evasion of Mycoplasma hyopneumoniae

As the main pathogen associated with enzootic pneumonia (EP), Mycoplasma hyopneumoniae (Mhp) is globally prevalent and inflicts huge financial losses on the worldwide swine industry each year. However, the pathogenicity of Mhp has not been fully explained to date. Mhp invasion usually leads to long-term chronic infection and persistent lung colonization, suggesting that Mhp has developed effective immune evasion strategies. In this review, we offer more detailed information than was previously available about its immune evasion mechanisms through a systematic summary of the extant findings. Genetic mutation and post-translational protein processing confer Mhp the ability to alter its surface antigens. With the help of adhesins, Mhp can achieve cell invasion. And Mhp can modulate the host immune system through the induction of inflammation, incomplete autophagy, apoptosis, and the suppression of immune cell or immune effector activity. Furthermore, we offer the latest views on how we may treat Mhp infections and develop novel vaccines.

Recent Advances of Engineered Cell Membrane-Based Nanotherapeutics to Combat Inflammatory Diseases

An immune reaction known as inflammation serves as a shield from external danger signals, but an overactive immune system may additionally lead to tissue damage and even a variety of inflammatory disorders. By inheriting biological functionalities and serving as both a therapeutic medication and a drug carrier, cell membrane-based nanotherapeutics offer the potential to treat inflammatory disorders. To further strengthen the anti-inflammatory benefits of natural cell membranes, researchers alter and optimize the membranes using engineering methods. This review focuses on engineered cell membrane-based nanotherapeutics (ECMNs) and their application in treating inflammation-related diseases. Specifically, this article discusses the methods of engineering cell membranes for inflammatory diseases and examines the progress of ECMNs in inflammation-targeted therapy, inflammation-neutralizing therapy, and inflammation-immunomodulatory therapy. Additionally, the article looks into the perspectives and challenges of ECMNs in inflammatory treatment and offers suggestions as well as guidance to encourage further investigations and implementations in this area.

Chimeric proteins of Mycoplasma hyopneumoniae as vaccine and preclinical model for immunological evaluation

Mycoplasma hyopneumoniae (M. hyopneumoniae) is a primary agent of porcine enzootic pneumonia, a disease that causes significant economic losses to pig farming worldwide. Commercial vaccines induce partial protection, evidencing the need for a new vaccine against M. hyopneumoniae. In our work, three chimeric proteins were constructed, composed of potentially immunogenic domains from M. hyopneumoniae proteins. We designed three chimeric proteins (Q1, Q2, and Q3) based on bioinformatics analysis that identified five potential proteins with immunogenic potential (MHP418, MHP372, MHP199, P97, and MHP0461). The chimeric proteins were inoculated in the murine model to evaluate the immune response. The mice vaccinated with the chimeras presented IgG and IgG1 against proteins of M. hyopneumoniae. There was induction of IgG in mice immunized with Q3 starting from 30 days post-vaccination, and groups Q1 and Q2 showed induction at 45 days. Mice of the group immunized with Q3 showed the production of IgA. In addition, the mice inoculated with chimeric proteins showed a proinflammatory cytokine response; Q1 demonstrated higher levels of TNF, IL-6, IL2, and IL-17. In contrast, animals immunized with Q2 showed an increase in the concentrations of TNF, IL-6, and IL-4, whereas those immunized with Q3 exhibited an increase in the concentrations of TNF, IL-6, IL-10, and IL-4. The results of the present study indicate that these three chimeric proteins can be used in future vaccine trials with swine because of the promising antigenicity.

Regulatory functional role of NLRP3 inflammasome during Mycoplasma hyopneumoniae infection in swine

Mycoplasma hyopneumoniae causes enzootic pneumonia, a highly contagious respiratory disease in swine that causes significant economic losses worldwide. It is unknown whether the nucleotide oligomerization domain-like receptor (NLR) family pyrin domain containing 3 (NLRP3) inflammasome regulates the immune response in swine during M. hyopneumoniae infection. The current study utilized an in vivo swine model of M. hyopneumoniae infection to investigate the regulatory functional role of the NLRP3 inflammasome during M. hyopneumoniae infection. Notable histopathological alterations were observed in M. hyopneumoniae-infected swine tissues, which were associated with an inflammatory response and disease progression. Swine M. hyopneumoniae infection was associated with an increase in the expression of the NLRP3 inflammasome, which stimulated pro-inflammatory cytokines such as tumor necrosis factor-alpha, interleukin 18, and interleukin 1 beta (IL-1β). The impact of the NLRP3 inhibitor, MCC950 on NLRP3 and pro-inflammatory cytokines in M. hyopneumoniae-infected swine was examined to investigate the relationship between the NLRP3 inflammasome and M. hyopneumoniae infection. Taken together, our findings provide strong evidence that the NLRP3 inflammasome plays a critical regulatory functional role in M. hyopneumoniae infection in swine.

Oral Immunization with Attenuated Salmonella Choleraesuis Expressing the P42 and P97 Antigens Protects Mice against Mycoplasma hyopneumoniae Challenge

Mycoplasma hyopneumoniae (M. hyopneumoniae, Mhp) is the etiological agent of swine enzootic pneumonia (EP), which has been associated with considerable economic losses due to reduced daily weight gain and feed efficiency. Adhesion to the cilia is important for Mhp to colonize the respiratory epithelium. Therefore, a successful vaccine must induce broad Mhp-specific immune responses at the mucosal surface. Recombinant attenuated Salmonella strains are believed to act as powerful live vaccine vectors that are able to elicit mucosal immune responses against various pathogens. To develop efficacious and inexpensive vaccines against Mhp, the immune responses and protection induced by recombinant attenuated Salmonella vaccines based on the P42 and P97 antigens of Mhp were evaluated. In general, the oral inoculation of recombinant rSC0016(pS-P42) or rSC0016(pS-P97) resulted in strong mucosal immunity, cell-mediated immunity, and humoral immunity, which was a mixed Th1/Th2-type response. In addition, the levels of specific IL-4 and IFN-γ in the immunized mice were increased, and the proliferation of lymphocytes was also enhanced, confirming the production of a good cellular immune response. Finally, both vaccine candidate strains were able to improve the weight loss of mice after a challenge and reduce clinical symptoms, lung pathological damage, and the inflammatory cell infiltration. These results suggest that the delivery of protective antigens with recombinant attenuated Salmonella vectors may be an effective means by which to combat Mhp infection. IMPORTANCE Mhp is the main pathogen of porcine enzootic pneumonia, a highly infectious and economically significant respiratory disease that affects pigs of all ages. As the target tissue of Mhp infections are the mucosal sites of the respiratory tract, the induction of protective immunity at the mucosal tissues is the most efficient strategy by which to block disease transmission. Because the stimulation of mucosal immune responses is efficient, Salmonella-vector oral vaccines are expected to be especially useful against mucosal-invading pathogens. In this study, we expressed the immunogenic proteins of P42 and P97 with the attenuated Salmonella Choleraesuis vector rSC0016, thereby generating a low-cost and more effective vaccine candidate against Mhp by inducing significant mucosal, humoral and cellular immunity. Furthermore, rSC0016(pS-P42) effectively prevents Mhp-induced weight loss and the pulmonary inflammation of mice. Because of the effectiveness of rSC0016(pS-P42) against Mhp infection in mice, this novel vaccine candidate strain shows great potential for its use in the pig breeding industry.

Development of a Multi-Epitope Vaccine for Mycoplasma hyopneumoniae and Evaluation of Its Immune Responses in Mice and Piglets

Mycoplasma hyopneumoniae (Mhp), the primary pathogen causing Mycoplasma pneumonia of swine (MPS), brings massive economic losses worldwide. Genomic variability and post-translational protein modification can enhance the immune evasion of Mhp, which makes MPS prone to recurrent outbreaks on farms, even with vaccination or other treatments. The reverse vaccinology pipeline has been developed as an attractive potential method for vaccine development due to its high efficiency and applicability. In this study, a multi-epitope vaccine for Mhp was developed, and its immune responses were evaluated in mice and piglets. Genomic core proteins of Mhp were retrieved through pan-genome analysis, and four immunodominant antigens were screened by host homologous protein removal, membrane protein screening, and virulence factor identification. One immunodominant antigen, AAV27984.1 (membrane nuclease), was expressed by E. coli and named rMhp597. For epitope prioritization, 35 B-cell-derived epitopes were identified from the four immunodominant antigens, and 10 MHC-I and 6 MHC-II binding epitopes were further identified. The MHC-I/II binding epitopes were merged and combined to produce recombinant proteins MhpMEV and MhpMEVC6His, which were used for animal immunization and structural analysis, respectively. Immunization of mice and piglets demonstrated that MhpMEV could induce humoral and cellular immune responses. The mouse serum antibodies could detect all 11 synthetic epitopes, and the piglet antiserum suppressed the nuclease activity of rMhp597. Moreover, piglet serum antibodies could also detect cultured Mhp strain 168. In summary, this study provides immunoassay results for a multi-epitope vaccine derived from the reverse vaccinology pipeline, and offers an alternative vaccine for MPS.

Characteristics of Mycoplasma hyopneumoniae Strain ES-2 Isolated From Chinese Native Black Pig Lungs

Mycoplasma hyopneumoniae is the primary pathogen of swine enzootic pneumonia and causes great economic losses to the swine industry worldwide. In China, M. hyopneumoniae seriously hinders the healthy development of the native black pigs. To prevent and treat porcine respiratory disease caused by M. hyopneumoniae, the characteristics of M. hyopneumoniae strain ES-2 isolated from Chinese native black pig lungs with gross lesions at post-mortem were studied for the first time in this study. Strain ES-2 cell was round or oval cells and most sensitive to kanamycin. The diameters of most strain ES-2 cells ranged from 0.4 to 1.0 μm with maximum viability of 1010 CCU/ml. Experimental challenge of animals with strain ES-2 showed respiratory disease could be reproduced, with pneumonic lung lesions evident. Comparative genomics analysis identified that 2 genes are specific to pathogenic M. hyopneumoniae strains, which may be predicted to be a molecular marker. These findings suggest that the study on the characteristics of M. hyopneumoniae strain ES-2 will guide the rapid and accurate drug use in the clinic, and develop a theoretical foundation for accurately diagnosing and treating the infection caused by pathogenic M. hyopneumoniae.

Development of an indirect competitive enzyme linked immunosorbent assay for the quantitative detection of Mycoplasma hyopneumoniae during the vaccine production process

Inactivated Mycoplasma hyopneumoniae vaccine is used extensively to control M. hyopneumoniae infection worldwide. Quantification techniques are essential in the process of standardizing and validating vaccines. In this study, we developed and optimized an indirect competitive enzyme linked immunosorbent assay (ic-ELISA) for the rapid quantification of M. hyopneumoniae antigen during vaccine production. Briefly, whole M. hyopneumoniae antigen was coated onto microtiter plates, and a polyclonal antibody against M. hyopneumoniae recombinant elongation factor thermo unstable (EF-Tu) protein was prepared and added with the samples to be tested. The methods were optimized and showed significant reproducibility, with coefficients of variation of 4.01% and 6.14% for the intra-and inter-assays, respectively. Quantification of M. hyopneumoniae cultures at different growth stages using the ic-ELISA test showed a similar curve to that of the traditional color changing units (CCU) assay, with a delay in the time when the amount reached the peak and started to fall. In the inactivated vaccine production process, the cultures could be harvested later than that for the live vaccine, at about 12 h after the end of the logarithmic growth phase. Different batches of cultures were measured for their relative potency value compared with the in-house reference vaccine, which was used to determine whether the cultures met the antigen amount requirements for vaccine preparation. The curves of the CCU titer and ic-ELISA titer in the logarithmic phase correlated strongly and a linear regression equation was established to calculate the CCU values rapidly using the ic-ELISA results. In conclusion, an ic-ELISA method was established to rapidly assess the amount of antigen in an M. hyopneumoniae culture during the vaccine production process.

Pathogenicity & virulence of Mycoplasma hyopneumoniae

Mycoplasma hyopneumoniae: is the etiological agent of porcine enzootic pneumonia (EP), a disease that impacts the swine industry worldwide. Pathogen-induced damage, as well as the elicited host-response, contribute to disease. Here, we provide an overview of EP epidemiology, control and prevention, and a more in-depth review of M. hyopneumoniae pathogenicity determinants, highlighting some molecular mechanisms of pathogen-host interactions relevant for pathogenesis. Based on recent functional, immunological, and comparative “omics” results, we discuss the roles of many known or putative M. hyopneumoniae virulence factors, along with host molecules involved in EP. Moreover, the known molecular bases of pathogenicity mechanisms, including M. hyopneumoniae adhesion to host respiratory epithelium, protein secretion, cell damage, host microbicidal response and its modulation, and maintenance of M. hyopneumoniae homeostasis during infection are described. Recent findings regarding M. hyopneumoniae pathogenicity determinants also contribute to the development of novel diagnostic tests, vaccines, and treatments for EP.

Long-Residence Pneumonia Vaccine Developed Using PEG-Grafted Hybrid Nanovesicles from Cell Membrane Fusion of Mycoplasma and IFN-γ-Primed Macrophages

CD8⁺ T cell responses play a critical regulatory role in protection against mycoplasma infection-related respiratory diseases. Nanovesicles derived from cell membranes have been shown to induce CD8⁺ T cell responses. Moreover, the short residence time of mycoplasma membrane-related vaccines in local lymph nodes limits the efficacy of current mycoplasma vaccines. Here, a long-residence pneumonia vaccine is developed using nanovesicles prepared by cell membrane fusion of Mycoplasma hyopneumoniae and interferon-γ (IFN-γ   )-primed macrophages, which are grafted with polyethylene glycol to increase residence time in the lymph nodes. Upregulation of intercellular adhesion molecule-1 (ICAM-1) on the membrane of IFN-γ-primed macrophages increases the targeting of the hybrid nanovesicle vaccine to the local lymph nodes, with increased CD8⁺ T cell activation. A mechanistic study reveals that CD8⁺ T cell activation is achieved via a pathway involving upregulation of C-C motif chemokine ligand 2/3 expression by E26 transformation-specific sequences, followed by increased immune-stimulatory activity of dendritic cells. In vivo, prophylactic testing reveals that the hybrid nanovesicle vaccine triggers a long-term immune response, as evidenced by a memory CD8⁺ T cell response against mycoplasma infection. The current study provides a new design strategy for mycoplasma vaccines that involves a hybrid method using biological sources and artificial modification.

Attenuation of Mycoplasma hyopneumoniae Strain ES-2 and Comparative Genomic Analysis of ES-2 and Its Attenuated Form ES-2L

Mycoplasma hyopneumoniae causes swine respiratory disease worldwide. Due to the difficulty of isolating and cultivating M. hyopneumoniae, very few attenuated strains have been successfully isolated, which hampers the development of attenuated vaccines. In order to produce an attenuated M. hyopneumoniae strain, we used the highly virulent M. hyopneumoniae strain ES-2, which was serially passaged in vitro 200 times to produce the attenuated strain ES-2L, and its virulence was evidenced to be low in an animal experiment. In order to elucidate the mechanisms underlying virulence attenuation, we performed whole-genome sequencing of both strains and conducted comparative genomic analyses of strain ES-2 and its attenuated form ES-2L. Strain ES-2L showed three large fragment deletion regions including a total of 18 deleted genes, compared with strain ES-2. Analysis of single-nucleotide polymorphisms (SNPs) and indels indicated that 22 dels were located in 19 predicted coding sequences. In addition to these indels, 348 single-nucleotide variations (SNVs) were identified between strains ES-2L and ES-2. These SNVs mapped to 99 genes where they appeared to induce amino acid substitutions and translation stops. The deleted genes and SNVs may be associated with decreased virulence of strain ES-2L. Our work provides a foundation for further examining virulence factors of M. hyopneumoniae and for the development of attenuated vaccines.

Development of an ELISA for distinguishing convalescent sera with Mycoplasma hyopneumoniae infection from hyperimmune sera responses to bacterin vaccination in pigs

Vaccination with inactivated bacterin is the most popular and practical measure to control enzootic pneumonia. After immunisation with inactivated bacterin, Mycoplasma hyopneumoniae colonised on the respiratory tract and lung stimulates the humoural immune responses and produces IgG and IgA antibodies. ELISA is a widely used serological method to detect M. hyopneumoniae antibodies. However, commercial IgG‐ELISA kit cannot distinguish between inactivated bacterin‐induced hyperimmune sera and convalescent sera stimulated by natural infection. SIgA‐ELISA method needs to collect nasal swabs, but collecting nasal swabs is not easy to operate. Establishment of a discriminative ELISA detecting humoural IgG from convalescent sera but not hyperimmune sera facilitates to evaluate the natural infection of M. hyopneumoniae after inactivated bacterin vaccination. We expressed and purified a recombinant protein named Mhp366‐N which contains an epitope recognised by the convalescent sera but not hyperimmune sera. The developed discriminative IgG‐ELISA could discriminate between inactivated bacterin‐induced hyperimmune sera and convalescent sera and was reproducible, sensitive and specific to M. hyopneumoniae antibody produced by natural infection. Compared to SIgA‐ELISA method, discriminative IgG‐ELISA was more convenient to detect IgG antibody from sera than IgA from nasal swabs, although it has limited sensitivity in the early stages of infection. Additionally, to some extent, it has a potential to avoid the interference of maternally derived IgG antibodies. The established discriminative IgG‐ELISA was efficient to judge the serological IgG antibodies induced from natural infection or inactivated vaccine stimulation and provided a useful method to investigate and evaluate the live organism infection after the application of inactivated bacterin.

Genomic Variability and Post-translational Protein Processing Enhance the Immune Evasion of Mycoplasma hyopneumoniae and Its Interaction With the Porcine Immune System

Mycoplasma hyopneumoniae (M. hyopneumoniae, Mhp) is a geographically widespread and economically devastating pathogen that colonizes ciliated epithelium; the infection of Mhp can damnify the mucociliary functions as well as leading to Mycoplasma pneumonia of swine (MPS). MPS is a chronic respiratory infectious disease with high infectivity, and the mortality can be increased by secondary infections as the host immunity gets down-regulated during Mhp infection. The host immune responses are regarded as the main driving force for the disease development, while MPS is prone to attack repeatedly in farms even with vaccination or other treatments. As one of the smallest microorganisms with limited genome scale and metabolic pathways, Mhp can use several mechanisms to achieve immune evasion effect and derive enough nutrients from its host, indicating that there is a strong interaction between Mhp and porcine organism. In this review, we summarized the immune evasion mechanisms from genomic variability and post-translational protein processing. Besides, Mhp can induce the immune cells apoptosis by reactive oxygen species production, excessive nitric oxide (NO) release and caspase activation, and stimulate the release of cytokines to regulate inflammation. This article seeks to provide some new points to reveal the complicated interaction between the pathogen and host immune system with Mhp as a typical example, further providing some new strategies for the vaccine development against Mhp infection.

Immune responses induced by a combined vaccination with a recombinant chimera of Mycoplasma hyopneumoniae antigens and capsid virus-like particles of porcine circovirus type 2

BACKGROUND

Mycoplasma hyopneumoniae (Mhp) and porcine circovirus type 2 (PCV2) are two important pathogens causing Mycoplasma pneumonia of swine (MPS) and porcine circovirus diseases and porcine circovirus-associated diseases (PCVDs/PCVADs), respectively, and resulted in considerable economic loss to the swine industry worldwide. Currently, vaccination is one of the main measures to control these two diseases; however, there are few combination vaccines that can prevent these two diseases. To determine the effect of combination immunization, we developed capsid-derived (Cap) virus-like particles (VLPs) of PCV2 and a new recombinant chimera composed of the P97R1, P46, and P42 antigens of Mhp. Then we investigated the immune responses induced by the immunization with this combination vaccine in mice and piglets.

RESULTS

The high level antibodies against three protein antigens (P97R1, P46, and P42 of Mhp) were produced after immunization, up to or higher than 1:400,000; the antibody levels in Pro group continuously increased throughout the 42 days for all the antigens tested. The lymphocyte proliferative response in PCV2 group was stronger than that in PBS, VP, Mhp CV in mice. The antibody levels for Cap remained stable and reached the peak at 35 DAI. The IFN-γ and IL-4 in sera were significantly enhanced in the Pro group than that in the negative control-VP group on Day 14 and 28 post-the first immunization in piglets.

CONCLUSIONS

Above all, the combination immunization could induce humoral and cellular immune responses against all four antigens in mice and piglets. Therefore, our approach is a simple and effective vaccination strategy to protect pigs against MPS and PCVD/PCVAD.

A Dual Swine Challenge With Porcine Circovirus Type 2 (PCV2) and Mycoplasma hyopneumoniae Used to Compare a Combination of Mixable Monovalent PCV2 and Monovalent M. hyopneumoniae Vaccines With a Ready-to Use PCV2 and M. hyopneumoniae Bivalent Vaccine

The present study evaluated the efficacy of swine vacciation using a combination of mixable monovalents for porcine circovirus type 2 (PCV2) and Mycoplasma hyopneumoniae against a ready-to-use bivalent vaccine under experimental conditions. Pigs at 21 days of age were administered either a combination of two mixable monovalent vaccines or a bivalent vaccine containing PCV2 and M. hyopneumoniae. Vaccination was followed with an M. hyopneumoniae challenge at 42 days of age (−14 days post challenge, dpc) and a PCV2d challenge at 56 days of age (0 dpc). Each vaccinated and challenged group was compared with the unvaccinated and challenged group for clinical, microbiological, immunologic, and pathologic differences. Clinically, two vaccinated and challenged groups showed minimal respiratory diseases that was characterized by occasionally coughing and sneezing. A significant difference was not calculated in the average daily weight gain, nasal shedding of M. hyopneumoniae, and pathological lesions between two vaccinated and challenged groups. A combination of two monovalent vaccines mixed into a combo prior to vaccination followed by challenge resulted in increased numbers of PCV2d-specific interferon-γ secreting cells at 21 dpc and a significant reduction in PCV2d viremia at 14 dpc when compared with the ready-to-use bivalent-vaccinated and challenged groups. These results offer supporting evidence that vaccination during the weaning to finishing period against M. hyopneumoniae and PCV2 is efficacious for controlling diseases caused by these two pathogens.

Antimicrobial treatment of Mycoplasma hyopneumoniae infections

Mycoplasma hyopneumoniae (M. hyopneumoniae) is the primary agent of enzootic pneumonia, a chronic and economically important respiratory disease of pigs. Control and prevention of M. hyopneumoniae infections can be accomplished by optimization of management and housing conditions, and by vaccination. The present paper summarizes the current knowledge on the main characteristics and efficacy of antimicrobials used for the treatment of clinical M. hyopneumoniae infections, the in vitro and in vivo activities of these antimicrobials and the reported resistance mechanisms against some. Potentially active antimicrobials against M. hyopneumoniae include tetracyclines, macrolides, lincosamides, pleuromutilins, amphenicols, aminoglycosides, aminocyclitols and fluoroquinolones. Antimicrobial treatment can be administered either orally or parenterally. Based on the overall results of efficacy studies performed under experimental and/or field conditions, the majority of agents belonging to these antimicrobial classes improved clinical parameters (clinical signs, lung lesions) and reduced performance losses due to M. hyopneumoniae infection. Antimicrobials may, however, not be able to prevent infection or to eradicate the bacterium from the respiratory tract. The decision to medicate should, therefore, be considered carefully. M. hyopneumoniae shows an intrinsic resistance against β-lactam antibiotics, sulfonamides and trimethoprim. A few reports have shown acquired antimicrobial resistance against some antibiotics, along with associated resistance mechanisms. The results of antimicrobial susceptibility testing are difficult to interpret in terms of treatment outcome, as no clinical breakpoints have been defined for M. hyopneumoniae.

Structure of P46, an immunodominant surface protein from Mycoplasma hyopneumoniae: interaction with a monoclonal antibody

Mycoplasma hyopneumoniae is a prokaryotic pathogen that colonizes the respiratory ciliated epithelial cells in swine. Infected animals suffer respiratory lesions, causing major economic losses in the porcine industry. Characterization of the immunodominant membrane-associated proteins from M. hyopneumoniae may be instrumental in the development of new therapeutic approaches. Here, the crystal structure of P46, one of the main surface-antigen proteins, from M. hyopneumoniae is presented and shows N- and C-terminal α/β domains connected by a hinge. The structures solved in this work include a ligand-free open form of P46 (3.1 Å resolution) and two ligand-bound structures of P46 with maltose (2.5 Å resolution) and xylose (3.5 Å resolution) in open and closed conformations, respectively. The ligand-binding site is buried in the cleft between the domains at the hinge region. The two domains of P46 can rotate with respect to each other, giving open or closed alternative conformations. In agreement with this structural information, sequence analyses show similarities to substrate-binding members of the ABC transporter superfamily, with P46 facing the extracellular side as a functional subunit. In the structure with xylose, P46 was also bound to a high-affinity (K_d = 29 nM) Fab fragment from a monoclonal antibody, allowing the characterization of a structural epitope in P46 that exclusively involves residues from the C-terminal domain. The Fab structure in the complex with P46 shows only small conformational rearrangements in the six complementarity-determining regions (CDRs) with respect to the unbound Fab (the structure of which is also determined in this work at 1.95 Å resolution). The structural information that is now available should contribute to a better understanding of sugar nutrient intake by M. hyopneumoniae. This information will also allow the design of protocols and strategies for the generation of new vaccines against this important swine pathogen.

Development of a Combined Genetic Engineering Vaccine for Porcine Circovirus Type 2 and Mycoplasma Hyopneumoniae by a Baculovirus Expression System

Mycoplasma hyopneumoniae (Mhp) and porcine circovirus type 2 (PCV2) are the main pathogens for mycoplasmal pneumonia of swine (MPS) and post-weaning multisystemic wasting syndrome (PMWS), respectively. Infection by these pathogens often happens together and causes great economic losses. In this study, a kind of recombinant baculovirus that can display P97R1P46P42 chimeric protein of Mhp and the capsid (Cap) protein of PCV2 was developed, and the protein location was identified. Another recombinant baculovirus was constructed without tag proteins (EGFP, mCherry) and was used to evaluate the immune effect in experiments with BALB/c mice and domestic piglets. Antigen proteins P97R1P46P42 and Cap were expressed successfully; both were anchored on the plasma membrane of cells and the viral envelope. It should be emphasized that in piglet immunization, the recombinant baculovirus vaccine achieved similar immunological effects as the mixed commercial vaccine. Both the piglet and mouse experiments showed that the recombinant baculovirus was able to induce humoral and cellular responses effectively. The results of this study indicate that this recombinant baculovirus is a potential candidate for the further development of more effective combined genetic engineering vaccines against MPS and PMWS. This experiment also provides ideas for vaccine development for other concomitant diseases using the baculovirus expression system.